Transmitting system



M1 19 2. E. A. LAPORT 1 2,214 211 TRANSMITTING SYSTEM Filed Nov. 16, 1940 9 Sheets-Sheet 1 Y 'WcHA/vA/EL INVENTOR EDMUND A. LAPORT A TTORNE Y Feb. 24, 1942. A, LAP RT 2,274,271 TRANSMITTING SYSTEM Filed Nov. 16, 1940 9 Sheets-Sheet 2 ANTENNA CURRENT 'INVENTOR EDMUND A. LAPORT 77 :9.

ATTQBNEY Filed Nbv. 1 6, 1940 9 Sheets-Sheet s mwk who. $1

- IN VENTOR. EDMUND A. LAPORT WW A TTORNE Y Feb. 24, 1942; A LAPQRT 2,274,271

I TRANSMITTING SYSTEM Filed NOV. 16, 1940 9 Sheets-Sheet 4 701v: R502. OSCILLATOR Fry. 4

0sc/L'LATOR ourpur E501 I E503 L '.J 'INVENTOR EDMUND A. LAPORT ATTORNEY Feb. 24, 1942. E. A. LAPORT 2,274,271

TRANSMITTING SYSTEM Feb. 24, 1942. E. A. LAPORT TRANSMITTING SYSTEM Filed Nov. 16, 1940 9 Sheets-Sheet 8 m E m k w l $3 3k A N am lb. m .25 uSRmQ w n. m 4 u N v w "a 1 a; 5 Qt H w g 8% J wnm H u a; a I l p w .Il. Mm g2 MR fink Mr NQD R: 3%; m m m m J 0. Sm J w Mn 38 N a N a N k i 8 & a Q v A C Q a a dddHHQ 3 3 3V Vd ZddJ-J J 3 VV V...v rJdJidJV w ning z 1, a4 uwuww ww a a 6 M i 9x536 fimbzkabb EDMUND L4. LAPORT 7% M ATTORNEY Feb. 24, 1942.- E; A LAPOR 2,274,271

TRANSMITTING SYSTEM vFiled Novv 16, 1940 9 Sheets-Sheet 9 9 THEM/ONE J F 504 A MIC TELEGRAPH REMOTE)? \9903 CONTROL ll k I T v.90! aye/1mm? supra/2 msausuc CHANGERSET 220w I 3m. k 25- k AUXILIARY RELAY INVENTOR EDMUND A. LAPORT Patented F eb. 24, 1942 FICE.

TRANSMITTING SYSTEM Edmund A.,Laport, Quebeaquebec, Canada, assignor to, Radio Corporation of America,a corporation of Delaware Application November 16, 1940, Serial No. 365,891 (01. 250-17) Claims.

My present; invention relates to radio transmitters. One broad object of my invention is to provide an improved general purpose highfrequency communication transmitter. Further general objects of my invention are to provide a transmitter having a wide frequency range; to provide a high frequency transmitter having a multiplicity of independent channels; to provide a transmitter which may be selectively'employed for different types of emission and to provide eificient switching means whereby the desired frequency of operation, channel and type of emission may be quickly chosen. Another more specific object is to provide an improved dialing system for carrying out the switching processes either locally at thetransmitter, or at some remote point.

Other objects, advantages and features of my present invention will appear as the more detailed description thereof proceeds.

up for cw operation. The third and fourth positions of the dial serve'to transmit respectively, three and four pulses and similarly, set vupthe transmitter for .operation on, however, theB Briefly, the transmitting system about to be described in greater detail consists of two radio frequency channels. Each channel includes a master oscillator which may be switched to either crystal or auto-excitation. Common intermediate and final power amplifier tubes are provided for the oscillation generators. ,A separate radiating system, however, is provided for each channel.

For CW or keyed carrier signalling, the output. of an audio oscillator is keyed in accordance with the signal to be transmitted. This keyed tone is rectified and employed to operate a keying relay which operates to block the oscillator and intermediate power stages of the transmitter.

For MCW signalling keyed, amplified. tone waves are fed to modulating tube system to modulate the plate and screen electrodes of the power amplifier tubes of the transmitter.

For telephonic or voice signalling, voice currents are similarly employed as in the MCW case channel. It is to be noted that when changing from MCW to telephonic signalling, a manually operated switch is thrown which disconnects the local oscillator and connects a microphone into circuit. The foregoing dialing and switching operations may be carried out locally at the transmitter or, as will be explained more fully hereinafter, by means of apparatus situated at a point remote from the transmitter.

Means, which will be explained more fully later, are provided at both local and remote points for causing proper sequential energization of the tubes in the transmitter.

Turning to the accompanying drawings:

Figure 1 is a wiring diagram of an oscillation generator and antenna system forming part of one channel of my transmitting system.

. Figure 2, similarly, is a wiring diagram of the oscillator and antenna of the other, or B channel,

of my transmitting system.

Figure 3 is a wiring diagram of the common intermediate and final power amplifier tube arrangement of my transmitter. By placing Figures 1, 2 and 3 together, along the lines XX and YY,'the complete wiring diagram for the entire radio frequency end of my transmitting system is obtained.

to plate and screen gridv modulate the power amplifier tubes. I

A dialing system is provided for quick changeover from one channel to another andalso from one type of transmission or modulation to another. Thus in the transmitter to be described, operating a dial of the automatic telephone type to its first position which transmits one pulse, sets up the transmitting system so that one channel, for example channel A, is operatively connected into circuit for MCW or telephonic opera tion. The second position of the dial whereby two impulses are transmitted, maintains the Figure 4 is a wiring diagram of the tone-generator, audio amplifier and modulating tubes used in connection with my transmitter.

" Figures 5 and 6 are wiring diagrams of control circuits for my transmitting system.

Figure 7 is a further diagram of power supply circuits and modulating elements used in conjunction with my transmitter.

Figure 8 is a wiring diagram of a rectifier supplying biasing potential for certain tubes of my transmitter. I

Figure 9 is a wiring diagram of a remote control unit which may be employed with my transmitting system.

Figure 10 is a wiring diagram of a frequency changer which may be used with my transmitter.

The letters A, B, C, D, E, F, G, H and P designate various terminal boards and indicate the manner in which Figures 1 to 8 inclusive, are to be connected together to form the complete transmitting system. For example, consider terminals I, 2, 3 and 4 within the rectangle or terminal board B (see Fig. 2). I Immediately below transmitter on channel A bu how venset it u I appears the legend ID. This means that terminal I on block B should be connected to terminal I on terminal block D (see Fig. 1). Similarly, terminal .2 on terminal board B (Fig. 2) has the legend I2C immediately beneath. This means that terminal 2 on board B of Fig. 2 is to be connected to terminal IE on rectangle or terminal block C (see Fig. 3), etc.

RADIO FRn UnNcY CHANNEL A Referring to Fig. 1, it will be seen that radio frequency channel A comprises a tube VMH. By means of a switch Still, crystal Ydfll may be switched across the grid resistor R403 so as to be in shunt to the grid and cathode of tube V40l. As illustrated the screen grid and suppressor are tied together and grounded through condenser C403. Regenerative feed-back takes place through condenser C408. With crystal control the plate circuit consists of coil L492 and condenser C498 connected in parallel and through condensers C464 and C485 to ground. An additional condenser C406 connected between plate and ground also forms part of the plate circuit. Condenser CW9 is made sufiiciently small sothat with the crystal removed from its holder or socket, the circuit fails to oscillate.

For increased flexibility switch Still permits operation of the oscillator tube at the same or different frequency without reliance upon the crystal for frequency control, Thus, when the switch is moved to the position indicated, the plate circuit described above, is effectively grounded at some intermediate point and the plate and control grid are connected to opposite terminals of condenser C488, it being noted that condenser 04% serves to block direct current voltage from the grid while permitting free passage of high frequency currents. Condenser C408 is arranged so as to be actuated by a bimetallic strip which causes its capacity to vary with changes in ambient temperature in such a way as to compensate drifts in frequency produced by changing temperature,

Output from oscillation generator Vail! is fed through condenser C491 and through switch S303 when thrown to its right-hand position to the grid of intermediate power amplifier tube 801. For channel A operation it will be understood, of course, that switch $3M is in its righthand position thereby connecting tuned circuit formed by condenser C ZH] and coil L403 to the plate of the intermediate power amplifier 881.

The output of the power amplifier iifl'l'is fed through condenser C395 in parallel to the grids of the paralleled final power amplifier stages or tubes 8|3. The latter, for channel A operation, are connected through switch sees and through switch S395 to the tuned channel A output circuit consisting of condenser CM! and coil L404 connected in parallel. The A channel antenna is connected to the output circuit by way of inductors 306 and 435 and condenser C432 as shown. I A

It is to be noted, referring to Fig. 1, that a segmental switch is provided for the condensers C4 I D and C4 in the output circuit of the power amplifiers. These condensers, by virtue of the switches, mounted on their shafts, are arranged so as to be completely removed from circuit, which is desirable for the highest frequency of operation. Other positions of the shaft enable preselected values of capacity to be added to the plate circuits and these, together with simultaneous adjustment of the plate circuit coils, al-

be conveniently shielded.

RADIO FREQUENCY CHANNEL B The B channel apparatus illustrated in Fig. 2 and operating through the common power amplifier tubes of Fig 3 is identical in all respects, except as to operating frequencies, to the apparatus and circuit of the A channel of Fig. 1. Hence, further detailed description of the B channel or Fig. 2 is deemed unnecessary. It will be noted, however, that corresponding elements in the B channel, have been marked with a 200 series rather than the 401]. series employed in connection with Fig. 1. Thus, for example, the crystal of Fig. 2 corresponding to crystal Y4fll, of Fig. 1, is Y20l of Fig. 2.

Also it is to be noted in connection with Fig. 3 that switches S3! to S396 inclusive, are mounted upon a common shaft, as indicated, which is electromagnetically operated by solenoids E30| and E302. Actuation of solenoid E302 places channel B into operation whereas operation of solenoid E3531 places channel A into operation.

AUoIo FREQUENCY Cmouirs The major portion of the audio frequency equipment used in connection with my improved transmitting system is shown in wiring diagram form in Fig. 4. Briefly, tube V50! is employed as a tone oscillator; tubes V532 and V583 are employed as audio amplifier tubes; tubes V5fi4 and V505 are used as class B modulators and tube V506 is used as part of an electronic switching system to cut off high frequency carrier currents in the absence of voice and MCW signals.

The tone oscillator tube Vfifil of Fig. 4 is provided with a tuned plate circuit including the right-hand winding of transformer Tiifll shunted by condenser CEBI. Feed-back is established through the upper left-hand secondary of the transformer. Output is taken from potentiometer R50! which operates as a, constant load for the oscillator. Condensers C513 and C5|2 are aud o frequency by-pass condensers. Condenser C5l4, however, is a radio frequency by-pass condenser for protective purposes. This condenser Icy-passes RF potentials which may be induced into unshielded key leads by radiation from the antenna. The output of the tone oscillator is connected in serles with the key jack J 802 (Fig. 5) and the keyed tone is then fed to the primary of transformer key 502 of Fig. 4. It is to be noted however, that as shown in Fig. 5, switch 8605i is in its upper position effectively connecting the microphone jack Jtiill of Fig. 5 to the primary of transformer T582 of Fig, 4. I

Signal waves fed through the secondary of transformer T592 are impressed as illustrated upon the control grid of tube V562 through a high-pass filter consisting of resistor 504 condensers c504 and c503 and inductance Ls'cl, so

remedied by the arranged as to by-pass to ground frequencies below 400 cycles. Since the plate circuit of tube V503--a beam tube-4s of high impedance, changes in loading produced by varying modulating grid currents causes distortion. This is inverse feed-back circuit through resistor I4 tothe cathode and suppressor electrodes of tube V502 which is a pentode type of tube. This inverse feed-back circuit lowers the effective plate impedance of tube V503 tosuch a value that its output is virtually independent of load variations, thus reducing the intrinsic distortion.

For voice and MCW signalling the amplified output of the audio amplifier appearing in the secondary of transformer T503 (Fig. 4) is used to turn on the carrier in whichever frequency channel of the transmitter is connected for operation, and also to plate and screen grid modulate the final power amplifier tubes.

Carrier power is put on the air in this way, it.

being noted that the purpose of this arrangement is to enable two-Way communication on the same carrier frequency. Voltage is taken from one of the modulator tube grids through condenser i the adjustable time constant circuit consisting of This voltage.

resistor R5; and condenser C5l I. is used in turn as control grid potential for the left-hand triode section of tube V506. In the presence of signal waves, current flow through the triode section syllabically operates relay E503. The contacts of this relay, when closed, impress,thr0ugh switch S] (Fig. 3) a positive voltage on the screen and suppressor grids, which are tied together in the oscillators of channels A or B; This positive voltage permits thegeneration of carrier wave oscillations. In the absence of signal waves, relay E503 (Fig. 4) opens, after a time interval determined by the adjustment of the time constant circuit R5l6, G5! I, of Fig. 4. Opening of the relay contact opens the screen grid-suppressor circuit of either oscillator A 'or B causing the oscillator to block.

In the same manner relay E50| (see Fig. 4) keys the transmitter telegraphically. Relay E50l is operatively placed into circuit by actuation of relay E502, in turn operated by dialing. Keying relay E50l (Fig. 4) is operatedby rectified grid current from the modulator tubes V504 and V505, which during CW keying are operated at zero plate voltage. It is to be noted that when relay E502 of Fig. 4 is operated the same dialing process operates relay E10l of Fig. 7, opening the direct current feed to the mid-point of one winding of transformer T104 and short-circuiting to the two secondary windings. Now re- 1 ferring to Fig. 4 again, under the last mentioned plate voltage. The amplified outputs of these modulator tubes are fed from the primary of transformer T104 (Fig. 7 into the two secondaries, the left-hand one of which impresses voltages on the screen grids and the right-hand one CONTROL Omonr'rs General The control circuits of the transmitter have been so designed that complete control is possible fr'om either the frontpanel of the transmitter, having thereon the controls of Fig. 5, which is designated as Local? control or from the remote control unit'of Fig. 9, which is designated jas' Remote control.

When operating the transmitter from a 220 volt 3 phase 25 cycle power source, rather than from a60 cycle source, complete control of the frequency changer of Fig. 10 is provided from both Local and Remote operating positions.

Thus, basically, four different types of control are possible. These are:

1. Local control on 60 cycles 2; Remote control on 60 cycles 3. Local control on 25 cycles 4. Remote control on 25 cycles The control sequence for each of these modes of operation willbe explained. In these analyses it isassumed that both radio frequency channels A and B are tuned and ready to operate.

Basically, the transmitter control relays may be divided into two general groups. The first group includes the D. C. relays which select and set up the circuits for either channel and for different types of emission. In the second group are the A. C. relays which perform the routine functions of starting, operating, overload protection and shutting down.

Local control on 60 cycles side marked 60 cycles, and the 110 volt 60 cycle supply connected to terminals 3 and 4 on {terminal block G. Terminals I, 2, 5 and 6 are used only for 25 cycle operation. Terminals 1 and 8 are for the telephone or control line when remote control is employed.

(1) Closure of the main power switch S10! (Fig. '1) located on the lower front panel applies line voltage to:

(a) The rectifier compartment heater circuit consisting of the'heater Rl0l (Fig; 6). and the thermostat EH1 (Fig. 6) which closes when the ambient temperature drops below +15 C. (b) The A. C. control circuit through fuses F103 and F104 (Fig.7). The A. C. relays are now ready to operate. when the interlocking D..C. relays are closed.

The primary of transformer Tl0l (Fig. 6), which supplies voltage to the copper oxide rectifier CR|0I (Fig. 6). This rectifier furnishes approximately 24 volts D. C. for the D. C. control relays. As the rectifier ages the output voltage will decrease since its internal resistance increases. To compensate for this decrease in voltage two additional taps arranged to supply a slightly higher voltage are provided on the secondary of TIM. 3

(2)1 Whenthe.oif-on switch S603 (Fig, 5 con- 1 trolling the. dialing, circuits. is closed it energizes the quick acting impulsing relay Ellll, (Fig. 6)..

(3) The closure of El Ill. energizes the quick make slow release relay El l2 (Fig. 6).

(5) When the auxiliary relay ElllQ closes, its NO (normally open) contacts energize El lll through the NC (normally closed) contacts of Em; the 60 cycle 'U link (Fig. 7) and the door interlock switches S102, S103 and S104 (Fig. 7)

(6) I The closure of Ellll is the first step in the sequence-of operation of the A.-C. relays and performs the following functions:

(a) Seals itself across the line independently of EH19 (Fig. 6) which previously closed EH.

(1)) Applies primary voltage to the filament transformer T'll'll (Fig. '7) and the bias transformer T8! (Fig. 8). The filaments of all tubes are now lighted and the bias power supply of Fig. 8 operating so that fixed bias is supplied to the tubes.

() Connects the coil of the time delay relay EIUZ (Fig. 6) across the line through the NC contact of Elll3. After a delay of approximately thirty seconds, to

permit the filaments of rectifier tubes 812 and 866 of Fig. 6 to reach proper operating temperature, the contacts of ElllZ close.

(7). The coil of EH16 is connected across the line through the NC. contact of El and one of the contacts of ElOl when the time delay relay contacts El02 close.

(8) When EH36 (Fig. 6) closes it seals itself across the line independently of EH12 and in addition:

(a) Energizes EH35 (b) Prepares the coil circuit of the plate contactor El [4 for closing.

(9) Closure of Elll5 transfers thecontacts of the time delay relay El02 from El'llfi, which has now sealed itself across the line, to EH14. This new circuit is used later for the shutting down sequence. EH14 is not energized since the NC contacts of El09 are now open.

(10) At this stage nothing more will happen until the dialing operation is executed. The circuits are now ready for the selection of channel A or B and the type of emission, This is accomplished by dialing local dial S602 (Fig. 5.)

(11) The dialing consists of dialing one to four impulses depending on the channel and type of emission desired. The number of impulses for each of the four dial posi- (12,) Dialing impulses are actually space intervals during which the control current to quick acting impulsing relay El ll! (Fig. 6) is momentarily broken. With each current interruption due to dialing, El lll opens, and on each drop out its back contacts momentarily close. This completes the ground return of the 24 volt circuit to the coil of the rotary stepping relay El l l and the anti-chatter relay EH3. Therefore, every time El l0 opens, El l l and El l3 receive a positive pulse of current. In a like manner, whenever the front contacts of El l0 close, El l2 receive a positive pulse of current.

(13') Relay EH2 is already closed (paragraph 3) and since it is a slow release relay it holds in during the impulsing action of El l6.

(14) The coil of the quick close slow release relay Ell3 is in parallel with the coil of El l l. Both of these coils receive the first impulse of current from El ll} through the home position of the stepping relay on the A bank of contacts. As soon as El l3 receives the first impulse of current it closes and maintains the circuit which would otherwise be opened as El l l moves off the home position. EH3 holds in for the duration of the positive pulses of current from El l0 so that both EH3 and Elll receive the pulses through the now closed NO contact on El i3.

(15) With every positive pulse of current the rotary stepping relay El ll advances one position. Depending on the number of impulses dialed El ll will move up from one to four positions to select the channel and type of emission desired.

(16) Since EH3 is a slow release relay it remains closed as long as it receives positive impulses from El ll]. In addition to scaling the impulsing circuit when El ll moves off the home position the closure of EH3 performs two additional functions: v

(a) Removes voltage from the B and 0 banks of contacts of El l I. This prevents chattering of the relays connected to those two banks of contacts as the rotary wiper passes the individual contacts during dialing.

(b) Opens the auxiliary relay Emil which in turn, opens the coil circuit of El M. This prevents plate and screen voltages from being applied to the circuits of the transmitter during dialing. This protects the channel switch contacts from arc-overs.

(17) After the impulsing dial S602 (Fig. 5) has returnedto rest EHO (Fig. 6) and EH2 f remain closed but EH3 falls out. Elll remains on positions one to four depending on the number of impulses received. I

(18) The dropping out of jEl l3 on the completion of dialing performs three functions:

(a) The circuit to the coils of El H and El I3 is opened and cannot be re-.

closed as long as EH2 remainsenergized. Therefore, further dialing does nothing to Elll or (b) 24 volts D.-C..1is againapplied to I the B and C banks of contacts of Elll (Fig. .6). Depending on the channel andemission dialed relays Ell (Fig. 6) and E502 (Fig. 4) will be energized if the stepping relay .wiper has stopped on their contact.

(c) Energizes El08,(Fig. 6) which in turn, prepares the circuit of the plate .contactor EH4 for closing when the plate ON switch 5604. (Fig. 5) switch'is: manually operated. and

normally closed except for test purposes. EH4 cannot be eneris closed. This .gized'unless the overload relay EH5 is in.

(19) The closure of the plate 'ON? switch S604 (Fig. 5) energizes EH4 (Fig. 6) which;

the high voltageitransiormer"T102 (Fig.

7) andintermediate voltagetransformer T103 (Fig. 7) Transformer T102 (Fig. 7) energizes rectifier tubes 812 (Fig. 6),

866 (Fig.' 6).

(20 When the high voltagebuilds up through its filter L'l0l, etc. 7-) it closes El03 (Fig. 6) which is' in series with the bleed- I erresistor R 'l0l Fig. 7). i (21) Closure of Ems Fig 6).removes line voltage from the coil of the time delay relay El 02 and transfers the coil to the nor:

mally closed contacts 'of EMS which is now open. The removal voltage from the coil of-El02 permits it to recycle al most instantly shouldthis needarise.

I (22). The transmitter isn owready for operation on the channel and type of emission as previously dialed';

(23). In step 15 1s was pointed out that El II will j of emission desired (see paragraph 11 and closes El0l.

i solenoid'iE30l (Fig. 3). (c) When El (Fig. 3) is energized it pulls the'channel switch assembly of F g. 3t0-the B position. Y

(b) Closure of El0'l (Fig. 6) energizes in turn, applies voltage to the primary or whereas transformer T103 energizes tubes.

(d) Just before the channel switch reaches the limit of its travel an arm (not shown) on the solenoid link strikes and opens the auxremoves voltage from the actuating solenoid E30l at the completion of the switching operation.

stops on .one of the first two positions, depending on the type of'emission'dialed (see paragraph 11),.and El0'l (Fig. 6) opens 1 (f) The. opening of El0'l energizes solenoid E302 (Fig. 3) which pulls the channelswitch to the A position.

. (9) At thecornpletion of the switching, operation S302 (Fig. 3) removes 'theline voltage from solenoid (h) It will be' noticed that whenever Elll (Fig. 6) returns to the homeffirst or second position, that El0l will open and cause the channel switch to move to w the A position. Therefore, whento be employed, or one frequency is t'o be used more than another, that frequency should be set up on the A channel. This will result in quieter operation and save wear and tear on the channel i switch. I

(24) Selection ofrthe type of emission is controlled by the B "bank of contacts on the stepping relay Ell I (Fig. 6). (a) When CW is dialed on dial S602 (Fig. 5) El l l stops on either the second or fourth position depending on the channel desired (see paragraph 11). "This energizes the CW-R/T-MCW selecj tion relay E502 (Fig. 4).

(1)) Closure ofjE502 connects the keyingrelay El into the grid bias andj disables the voice operated carrier control explained previ- M ously.; (0) When E'l0l (Fig. 7) closes it shorts the. secondaries of the modulation transformer T104 and removes plate voltage from the j modulator tubes. i '(d) "For cw operation the telephone- I T telegraph switch S606 (Fig. 5) must beset onftelegraph. This i applies plate voltage to the audio .'oscillator V50l (Fig. 4) which is used t'o'furnish the keying tone. "In addition it connects the audio oscillator to the input transformer T502 of the audio sys tem through transformer Tl I (Fig. 5).

(e) When R/T and MOW are dialed El ll (Fig. 6) stops on either the first or third position depending on the channel selected. This causes E502 (Fig. 4) to open or to remainopen when starting up.

, iliary' switch S302 (Fig. 3). This- (e)"When channel A is dialed Elll ever onlya single frequency is returnof the modulator tubes v (f) -Theopeningof E502 (Fig. 4) shorts thecoil otkeying relay E50] and removesthe short from the timing circuit of the voice operated carrier tube V506 (Fig. 4:).

EIUI (Fig. 7) also opens.

'(g') The opening of -Ellll removes the shorts from the secondaries of the modulation transformer T104 -and applies plate voltage to the modulators.

(h) Either-R/T or MCW is selected by means of the telephone-tele- .graph switch S606 (Fig. 'When'this switch is in the telephone .position it connects the microphone to the input circuits. In the telegraph position the keying audio oscillator V50l (Fig. 4) '-is energized and connected into theaud-ioinput circuits. To change channels or emission, a new dialing operation is' requ'ired. Return the f off-on toggle switch 8603 (Fig. 5) to r off for' app'r'oximately one second and:

then' reclose. This opening and reclosing of S603 is equivalent to momentarily hanging up the receiver before redialing on the familiar automatic public telephone. In other words, after a dialing operation iscompl'eted the dial is disabled "and further dialing will produce no change. To render the dial operative again, switch S603 must be moved to its off'position"for about one second and then returned to on.

(a) Opening-switch S663 (Fig.5) releases relay'El l 6 (Fig. 6) which permit's"relay"Ell2 'to drop out.

(o) "As soon as-El [2 drops out it opens EH19 whose NC contacts reclose and apply voltage to the coil of the time delay relay El02 through the NO contact of EH13.

(c) When EH2 (Fig. 6) drops out it also closes the circuit to the interrupter springs on the rotary switch El l l whose coil then rec'eives impulses from. these interrupter springs until the circuit is opened "when the bridging wiper on theD bank reaches the open contact at the home position. The interrupter springs operate in exactly the same man her as the contacts on a common door "bell iorbuzzer.

(d) Since the coilof relay El l3 (Fig. 6)

is inlparallel with the coil of Elli 'it-i's closed by the pulses from-the interrupter springs.

(e) EH3 closes on the first pulse received and in closing removes the 'voltage fromthe B and C banks of contacts of El I l and thus pre- 0 vents chattering of Elll'l, E562 and :E'llll as'the wiper moves around. The closing of EH3 opens EH16 which, in turn, opens the plate contactor El l4 removing high and intermediate voltage from the equipment. EH13 opens, but the coil of El02 still remains connected to the line through Ell) l.

(f E H l -stops irotating when it reaches then'ext home position since the automatic impulsing circuit is broken'by the open contact at that point on the D bank.

(9) After the last pulse has been received El l3 falls out. However, the auxiliary relay El 68 does not reclose, and re-apply high voltage to the circuits, since its return circuit has also been opened at'the home contact on D bank.

(72.) Reclosure of S663 (Fig. 5) causes the same sequence of starting operations as has been outlined, except that El'66 (Fig. 6) is already locked in and it is not necessary 'to' wait thirty seconds for-EH12 (Fig.6) to reclose. The "new dialing operation resets the selective c'ontrol circuits in the same 'manner as previously outlined.

(i) Onfthehompletio'n of the re-dialing sequence and intermediate voltage is immediately applied to "the circuits and the transmitter is ready for operation. EH13 (Fig. 6) closes and removes voltage from the time delay relay EH32 (Fig. 6) which then returns to its" starting position for the next starting cycle.

(-26) 1f S603 (Fig. 5) is opened and not reclosed within thirty seconds the transmitter shuts down in the following manner:

(a) The first part ofthe closing down sequence is the sameas outlined in paragraphs -25(a) and 25(9) inclusive. (b) EH12 (Fig. 6) continues to run until thirty seconds have elapsed, at which time its contacts close and energize EIM through the NC contacts of EH39 (Fig. 6)

(c) The closure of EH14 breaks the seal on EIOI (Fig. 6) which then opens.

(at) When EIDI (Fig. 6) opens it reremoves primary voltage from the filament transformer T'l0l (Fig. '7) and from the bias transformer Tl (Fig. 8).

(e) The opening of Ellll (Fig. 6) also breaks the seal on E106 which .now opens de-energizing EH15 (Fig. 6).

(f) All'circuits are now in their initial 'de-en'ergized condition corresponding to paragraph (1).

(27) When operating, standby may be dialed in the following manner:

(a) Return the oiT-on switch S663 (Fig.5) 'to the 01f position and then reclose. This sequence is the same as covered in paragraphs 25(a) and 25(h) inclusive. The transmitter is now on standby with filaments hot but with no high or intermediate voltage on any of the circuits.

(b), To come back on the air simply redial the frequency and emission desired and the transmitter is ready for immediate use. This action is covered in paragraph (28) When an overload occurs in the high voltage rectifier circuit, the overcurrent acts through the D.-C. coil for El l and through its NC contact releases El l4 which shuts off the intermediate and a n rectifiers. i

(29) Operation of El l5 (Fig. 6) on an overload causes its contact to be held open by a mechanical latch. El I5 is reset by dialing standby as outlined in paragraph 27 immediately above. The reset coil is energized whenever the rotary relay Elll returns to home position since the wiper arm on the C bank of contacts completes 'the circuit through one of the normally closed (NC) contacts on El l3. 4

REMOTECQNTRQL on 60 CYoLEs To control the transmitter from a remote loca- :tion it is necessary to use the remote control apparatus shown in Fig. 9, fully equipped withv Ll, L2 (Fig. 9) is connectedto terminals 1G and 8G (Fig. 7) and thence to IOF and HF (Fi 5). The remote-local switch S605 (Fig. 5) must be on remote. This connects the input transformer T502 (Fig. 4) to the telephone line and remote control.

When'operating on remote control the plate on-standby-switch S604 (Fig. 5) must be in the plate on position since there is not control of this switch from the remote point. S604 is intended primarily as an aid when testing or tuning up, standby when operating being obtained by dialing as described in paragraph 27 immediately above.

The main off-on S'l0l (Fig. '2) switch is left on at all times. This provides power for the control relays and heat, when necessary, for the.

rectifier tube compartment. This is important since the temperature of the rectifiers must always be above C. when operating. Since the automatic thermostat Ell! (Fig. 6) maintains the compartment at this minimum temperature when the cover is on, the transmitter is always ready to come on the air without delay even if the ambient temperature is as low as --40 C.

Control from the remote position is now the same as for local operation except that S602 and S603 (Fig. 5) have been replaced by S902 and S90l (Fig. 9). This description is covered above headed Local Control on 60 Cycles.

To provide a check on the operation of the control circuits from the remote'point the re- "mote line meter M99! (Fig. 9) is connected in the ground return circuit. This meter will read only when (a) The main power switch S10 I (Fig. 7) is closed (b) The remote-local switch S605 (Fig. 5) is on remote" (c) The telephone line and ground return circuit are connected and continuous LocAr. CONTROL ON 25 CYCLES .The transmitter can be operated from a 200 volt, Bphase, 25 cycle power supply when pro- 'videdwith. a frequency changer as shown in Fig. 10; This is a 220 volt, 3 phase, 25 cycle motor coupled to a 115 volt, single phase, cycle alternator, and field exciter, together with the necessary operating controls.

The four links, T, U, V, W (Fig. 7) on the main power terminal board should be shifted over to the side marked 25 cycles. The volt, 60 cycle supply'from the alternator connects to terminals IG and 2G while the 110 volt, 25 cycle supply from the transformer in the'frequencychanger connects to terminals 36 and AG. The magnetic starter and auxiliary relay are connected to terminals 5G and 6G. Terminals 1G and '8G are for the remote control line when used.

The remote-local. switch S605 (Fig. 5) should be in the .local position.

(1) Closure of the main power switch S10! (Fig. '7); located onthe lower front panel applies line voltage to:

' (a) The rectifier'compartment heater circuit consisting of the heater Rl0l. (Fig. 6) and the thermostat .Elll (Fig. 6) which closes when the ambient temperature drops below y+l5 C.

(b) .The primary of transformer El 0| (Fig. 6) which supplies voltage to I the. copper oxide rectifier CRl0l (Fig. 6). This rectifier furnishes approximately 24"volts D.-C. for the D.-C. control relays. (c) The frequencychanger control circuits through fuses F103 and F104.

(2) When the ,off-onfswitch ssos (Fig. 5) is closed it energizes the quick acting impulsfling relay Ellll. (3) The closure of EHO (Fig. 6) energizes the quick make slow release relay El l2 (Fig. 6). (4) Closureof El l2 performs three functions:

' (a) Completes the circuit to the coil of 'the'anti-chatter relay EH3 and to the coil of the rotary stepping relay El l I through the wiper and the "home contact on the A bank of Elll. These relays are now ready to receive dialing impulses; Y

v (b) Closes auxiliary relayElflQ.

(c) Opens the automatic homing circuit ofEl H to permit selective dialing.

(5) When the auxiliary relay El09 closes, its NO contacts. energize the 25 cycle relay El l6 through. th NC c nt ts of. 10

(6) Closure of El l6 which follows-.-

(a) Energizes the auxiliary relayEllllll (Fig. 10) which completes the circuit between the 60 cycle alternator and terminals IG and 2G.

(1)) Operates the line starter of the frequency changer which now comes up to operating speed.

('7 As the frequency changer accelerates, the

potential across IG and 2G increases closing El l through the U link, EH14 and the interlock switches.

(8) With 110 volts, 60 cycles now available on the A.-C. control circuits, the closure of El Ill (Fig. 6) corresponds to step (6) in the description of operation with Local control on 60 cycles. The remainder of the starting up and operating functions are identical to those described in that section.

(9 To shut down, ssus (Fig. is returned to ltofilli (10) Opening switch S603 (Fig. 3) releases relay Ellll (Fig. 6) which permits relay EH2 to drop out.

El 09 whose NC contacts reclose and apply voltage to the coil of the time delay relay EH32 through the NO contact of EH13.

WhenEl l2 (Fig. 6) drops out it also closes the circuit to the interrupter springs on the rotary switch Elll whose coil then receives impulses from these interrupter springs until the circuit is opened when the bridging wiper on the D bank reaches the open contact at the home position. The interrupter springs operate in exactly the same manner as the contacts 'on a common door bell or buzzer.

Since the coil of relay EH3 (Fig. 6) is in parallel with the coil of El ll it is closed by the pulses from theinterrupter springs.

El l3 (Fig. 6) closes on the first pulse received and in closing removes the voltage from the B and C banks of contacts of El l l and thus'prevents chattering of Elll'l (Fig. 6), E502 (Fig. 4) and E'Illl (Fig. 7) as the wiper moves around. The closing of El l3 opens EH38 which, in turn, opens the plate contactor El M (Fig. 6) removing high and intermediate voltage from the equipment. EH13 (Fig. 6) opens, but the coil of EH12 (Fig. 6) still remains connected to the line through Ellll (Fig. 6).

El ll (Fig. 6) stops rotating when it reaches the next home position since the automatic impulsing circuit is broken by the open contact at that point on the 1) bank. After the last pulse has been received El l3 (Fig. 6) falls out. However, the auxiliary relay EH18 (Fig.6) does not reclose, and reapply high voltage to the circuits, since its return circuit has also been opened at the home contact an D bank. ElllZ (Fig. 6) continues to run until thirty seconds have elapsed, at which time its contacts close and energize EH14 (Fig. 6) through the NC contacts of EH19 (Fig. 6). When Elfl l (Fig. 6) closes it breaks the circuit to El l6 which then drops out re- As soon as El l2 (Fig.6) drops out it opens -S90l (Fig. 9).

-(21) The opening of Ellll- (q) Removes primary voltage from the filament transformer Tllll (Fig. '7) and the bias transformer Tlllll (Fig. 8)

(b) Breaks the circuit to the coil of El l6 (Fig. 6) to prevent its closing when the NC contacts of El 64 (Fig. 6) reclose.

'(c) Breaks the seal on Elllli (Fig. 6)

which now opens tie-energizing El65 (Fig.6).

(22) The opening of Elll5 (Fig. 6) de-energizes ElM (Fig. 6) which now opens.

(23) All circuits are now in their initial de-energized condition corresponding to paragraph 1 under Local Control on 25 Cy cles.

REMOTE Connor. on 25 CYCLES The same remote control of Fig. 9 is used for 25 cycle remote operation as is used for cycle remote operation. The method of operation is identical.

All connections to the main power terminal board are the same as for local control on 25 cycle, except that the telephone line Ll, L2 (Fig. 9) is connected to terminals 1G and 8G.

The remote-local switch S665 (Fig. 5) must be on remote. This connects the input transformer T502 (Fig. 4) to the telephone line Ll, L2 and remote control of Fig. 9.

When operating from a remote point the plate on-standby switch S604 (Fig. 5) should be in the plate on position and the main power switch S'llll (Fig. 7) ON.

Control from the remote position is now the same for local operation, except that S602 and S603 (Fig. 5) have been replaced by S962 and This description is covered in section above labeled RemoteControl on 60 Cycles.

As far as the remote operator is concerned, operation on either 25 or 60 cycles is identical.

Having thus described my invention what I claim is:

1. A transmitting system comprising a plurality of radio frequency channels, each channel including an oscillation generator and a final tuned output circuit, a power amplifier system and means for selectively switching said power amplifier system from the oscillation generator and tuned output circuit of one channel to the oscillation generator and tuned output circuit of the other channel and means operatively associated with said switching means to ground both terminals of the output circuit of that channel which is not operatively connected to the power amplifying system.

2. A transmitting system comprising a plurality of radio frequency channels, each channel including an oscillation generator and a final tuned output circuit, a power amplifier system and means for selectively switching said power amplifier system from the oscillation generator and tuned output circuit of one channel'to the oscillation generator and tuned output circuit of the other channel, a modulating circuit connected to the power amplifying system for producing one type of signal emission, another modulating circuit connected to said oscillation generators to produce a difierent type of signal emission and means for selectively utilizing one of said modulating circuits to control the output of the operating channel of the transmitting system.

3. A transmitting system comprising a plurality of radio frequency channels, each channel including an oscillation generator and a final tuned output circuit, a power amplifier system and means for selectively switching said power amplifier system from the oscillation generator and tuned output circuit of one channel to the oscillation generator and tuned output circuit of the other channel, a modulating circuit adapted to be associated with the power amplifying system'for producing one type of signal emission, another modulating circuit adapted to be associated with said oscillation generators to produce a diiferent type of signal emission and means for selectively utilizing one of said modulating circuits to control the output of the operating channel of the transmitting system and impulse responsive means responsive to pre-selected munbers of impulses for selectively connecting the amplifier system to the oscillation generator and output circuit of any one of the channels and for selectively and operatively connecting one of said modulating circuits to the operating channel of the transmitting system.

4. The system, as claimed in claim 3, characterized in addition by the fact that one of said modulating circuits is adapted to modulate the output of the power amplifier system in accordance with audio frequency waves and being further characterized by the provision of additional means, operative in response to presence and absence'of audio signal waves, to turn on and off respectively the high frequency output of the amplifier system.

5. A transmitting system comprising a plurality of radio frequency channels, each channel I including an oscillation generator and a final tuned output circuit, a power amplifier system and means for selectively'switching said power amplifier system from the oscillation generator and tuned output circuit of one channel to the oscillation generator and tuned output circuit of the other channel, a modulatingcircuit adapted to be associated with the power amplifying system for producing one type of signal emission,

another modulating circuit adapted to be associated with said oscillation generators to produce a difierent type of signal emission and means for selectively utilizing one of said modulating circuits to control the output of the operating chan nel of the transmitting system and impulse responsive means responsive to pre-selected numbers of impulses for selectively connecting the amplifier system to the oscillation generator and output circuit of any one of the channels and for selectively and operatively connecting one of said modulating circuits to the operating channel of the transmitting system, a source of high voltage for said power amplifier system and means responsive to actuation of said impulse responsive means for preventing the application of high voltage to said amplifier until said impulse responsive means has completed the selective C0112- nection of the power amplifier system to a desired channel and the selective connection of a 9 modulating circuit to the channel connected for high frequency operation.

6. A transmitting system having a plurality of high frequency channels, an oscillation generator and a tuned output circuit for each channel, a tube amplifier, means for switching the tube amplifier to an oscillation generator and tuned circuit of a selected channel, a source of alternating current power, a plurality of modulating circuits, means to selectively and operatively connect one of said modulating circuits to the apparatus in the operating channel, a direct current operated dialing system, a low voltage rectifier for rectifying power derived from said source, means for connecting the rectifier to the dialing system whereby rectified power from said lowvoltage rectifier serves to place the dialing system in operative condition, a high power rectifier connected to said source and for supplying high voltage power to all tubes in the operating channel, means rendering said high power rectifier inoperative until the filaments of said high power rectifier and all tubes in the operating channel havebeen permitted to warm up for a period of time, disabling means operating after said dialing means has been operated once, to render further dialing inoperative as regards further switching of said tube amplifier and modulating circuits, and means operative at will to disable said disabling means whereby to render said dialing means operative again to selectively switch said tube amplifier and modulating circuits.

7. The system as claimed in claim 6 characterized by the fact that means are provided for grounding the terminals of the output circuit of a disabled channel.

8. Apparatus as claimed in claim 6 characterized by the provision of an overload relay responsive to overload on said tube amplifier system to remove voltage to be rectified from the high voltage rectifier and means including said dialing apparatus for resetting said overload relay.

9. A transmitting system comprising a plurality of radio frequency channels, each channel including an oscillation generator and a final tuned output circuit, a power amplifier system,

. and mean for selectively switching said power amplifier system from the oscillation generator and tuned output circuit of one channel to the oscillation generator and tuned output circuit of the other channel, an alternating current modulating circuit connected to the power amplifying system for amplitude modulating the waves transmitted by said transmitting system, a tone generator, a rectifier for Waves generated by said tone generator, and means responsive to said rectified waves for keying said oscillation generators with a code ignal, and means for selectively utilizing either the amplitude modulating means or the keying means for controlling the transmitted output of the transmitting system.

' EDMUND A. LAPORT. 

